ProjectSummary Mechanotransduction (MET) channels reside at the tips of inner ear hair?cell stereocilia, where they mediate the conversion of sound?induced mechanical stimuli into electrical signals that are transmitted to the brain. Theseminiaturemachinesopeninresponsetomechanicalchangeandallowaselectiveinfluxofcationsinto hair cells. Their molecular identity has already been pursued for over two decades. Excitingly, a number of membraneproteinshavebeenrecentlyimplicatedascriticalcomponentsoftheMETchannelcomplex:TMC1, TMHSandTMIE.Thedysfunctionofanyoftheseproteinsisassociatedwithhearingloss.Todate,strategies forpharmacologicalinterventionaregreatlylimited,partlyduetolackofourunderstandingoftheseproteins' respective role during mechanotranduction. The goal of this project is to illuminate these proteins' atomic structure,theirinterplay,andtheirmechanismoftheaction.Here,wewillintegrateexperimentaltechniques includingsingleparticlecryo?electronmicroscopy,proteinbiochemistryandengineering,inordertoprovidea detailed understanding of these proteins' mechanical and structural properties. Atomic structures will help identify the long?sought pore?forming domain of the MET channel, through which ion flux occurs. The structures will also help identify gating and regulatory domains, which may be key to modulating the ion channel function. By establishing a structural basis for the MET channel function and regulation, we expect thattheproposedresearchwillhelpindesignofnovelpharmaceuticalapproachesfortargetinghearingloss.